IN RATS AND GUINEA-PIGS. 



50 



45 



\ 



40 

 35 

 JO 



/S 



IO 

 5 



75' 

 7O 



60 



F< 



- 



\ 



\ 



\ 



\ 





4O 



JO. 



10 



B, 



\,A 



^ 



v 



\ 



\ 



\ 



\ 





14.5 



345 



745 



845 



Grade 4.5 



FIG. 3. Variation in extent of the back-stripe in lots A to F of hooded rats, showing the effects of cross- 

 breeding with rats of Irish pattern. The positions of the means are shown by vertical lines. 



